Poppet valve device

ABSTRACT

A poppet valve device according to the present invention is adapted to sequentially operate a plurality of poppet valves the switching operation of a pilot valve, for example, an electromagnetic solenoid or the like which operates in response to an external input signal. The above-mentioned poppet valve device includes first and second poppet valves (A, B) each of which is constructed so that a poppet (32) for communicating or intercepting an inlet port (30) and an outlet port (31) with or from each other may be moved towards a communicating position by an inlet port side pressure acting upon its pressure receiving portion (32a). The poppet (32) may be moved towards an intercepting position by a pressure acting upon its back pressure chamber (38a, 38b). A pilot valve (c) connects the respective back pressure chambers of these poppet valves to a tank (2) and includes a variable choke portion controlled by an external input signal so that the pressures at the respective back pressure chambers, when the respective poppets of the respective poppet valves are moved to the positions for communicating the respective inlet ports with the respective outlet ports, may be different from each other.

FIELD OF THE INVENTION

The present invention relates to a poppet valve device in which aplurality of poppet valves are operated to switch by switchingoperations of a pilot valve, and especially to a poppet valve device inwhich a plurality of poppet valves are sequentially operated to switchby switching operations of a pilot valve actuated by, for instance, anelectromagnetic solenoid or the like which operates in response to anexternal input signal.

BACKGROUND OF THE INVENTION

A poppet valve device, in which a pressure difference is producedbetween the front and the rear of a poppet in a poppet valve byswitching operations of a pilot valve, and thus the poppet is moved tooperate the poppet valve for switching, has been known.

With such a poppet valve device, although a plurality of poppet valvescan be simultaneously operated to switch by means of a single pilotvalve, it is impossible to sequentially operate a plurality of poppetvalves for switching.

Consequently, in the case where a plurality of poppet valves are to besequentially operated for switching, pilot valves are respectivelyprovided in correspondence to the respective poppet valves and provisionis made such that the timings for operating the respective pilot valvesfor switching are shifted to sequentially operate for switching, hencenot only a number of pilot valves is increased and a cost becomes high,but also the plurality of pilot valves must be sequentially operated forswitching, and the operations would become very troublesome.

SUMMARY OF THE INVENTION

The present invention has been worked out in view of the above-mentionedcircumstance, and one object of the invention is to provide a poppetvalve device in which provision is made such that a plurality of poppetvalves can be sequentially operated for switching by switchingoperations of a single pilot valve.

Another object of the present invention is to provide a poppet valvedevice, in which two, first and second, poppet valves are provided, andamong these, a pressure on the outlet side of the first poppet valve canbe made to be a preset pressure.

In order to achieve the above-mentioned objects, according to a firstaspect of the present invention, there is provided a poppet valve devicecomprising at least two, first and second, or more, that is, a pluralityof poppet valves, each of which is constructed in such manner that apoppet for communicating or intercepting an inlet port and an outletport formed on one side of a cylindrical body fitted within a valve boremay be moved towards a communicating position by a pressure on the inletport side acting upon its pressure receiving portion, while it may bemoved towards an intercepting position by a pressure acting upon itsback pressure chamber, and a pilot valve which connects the backpressure chambers of the respective ones of the aforementioned pluralityof poppet valves to a tank, and which includes a variable choke portioncontrolled by an external input signal so that the pressures in therespective back pressure chambers when the respective poppets in theaforementioned respective poppet valves are moved to the positions forcommunicating the respective inlet ports with the respective outletports may be made different from one another.

According to a second aspect of the present invention, there is provideda poppet valve device as described above in connection to the firstaspect, wherein the poppet of the aforementioned first poppet valve ismounted so as to be freely slidable along a smaller diameter cylindricalbody of an axial body fitted within the above-mentioned cylindrical bodyfrom the other side of the cylindrical body, and is biased towards theabove-mentioned intercepting position by a resilient force of acompression spring interposed between the above-mentioned axial body andthe poppet, and the inner diameters of the respective ones of theaforementioned outlet port and the above-described poppet are madeidentical.

According to a third aspect of the present invention, there is provideda poppet valve device as described above in connection to the firstaspect, wherein a valve opening pressure in the back pressure chamberwhen the poppet in the aforementioned first poppet valve is movedtowards the above-described communicating position, is set lower than avalve-opening pressure of the above-mentioned second poppet valve.

According to a fourth aspect of the present invention, there is provideda poppet valve device as described above in connection to the firstaspect, wherein the poppet in the aforementioned first poppet valveincludes a back pressure chamber to which the pressure at its outletport is introduced via a narrow hole drilled at the head portion of thepoppet so that the above-mentioned poppet may be biased towards theintercepting position by the pressure at the outlet port, and a largerdiameter portion formed integrally at the tip end portion of theaforementioned poppet valve so as to offset a pressing force in thedirection directed to the communicating position of the above-describedpoppet caused by the pressure at the outlet port acting upon a seatsurface of the poppet in the aforementioned first poppet valve.

According to a fifth aspect of the present invention, there is provideda poppet valve device as described above in connection to the firstaspect, which comprises two, first and second poppet valves whose backpressure chambers are communicated with their tank sides so that thepressure acting upon the respective back pressure chambers may serve asa tank side pressure and also communicated with the inlet port sides viachokes, and a pilot valve including variable choke portions providedbetween the above-mentioned first and second poppet valves and a tankand controlled by an external input signal, wherein the construction issuch that if the outlet side pressure of the above-mentioned firstpoppet valve becomes a preset pressure or higher, the inlet port and theoutlet port of the aforementioned first poppet valve are interceptedfrom each other, whereas when the pressure in the back pressure chamberin the aforementioned second poppet valve causes the poppet in theaforementioned first poppet valve to come at the communicating position,if it becomes a lower pressure than the pressure in the back pressurechamber in the first poppet valve, the inlet port and the outlet port ofthe above-mentioned second poppet valve may be communicated with eachother.

According to a sixth aspect of the present invention, there is provideda poppet valve device as described above in connection to the thirdaspect, wherein the inlet port of the aforementioned first poppet valvecommunicated with a boom raising pressure chamber in a boom cylinder ofa construction machine such as a power shovel, and the outlet portcommunicates with a boom lowering pressure chamber in theabove-mentioned boom cylinder.

According to a seventh aspect of the present invention, there isprovided a poppet valve device as described above in connection to thefourth aspect, wherein the inlet port of the aforementioned first poppetvalve communicates with a boom raising pressure chamber in a boomcylinder of a construction machine such as a power shovel, and theoutlet port communicates with a boom lowering pressure chamber in theaforementioned boom cylinder.

According to an eighth aspect of the present invention, ther is provideda poppet valve device as described above in connection to the firstaspect, wherein the aforementioned first poppet valve includes a rodbody fitted in an inner bore of the poppet from the base end side of thesame poppet via a compression spring, an axial rod inserted from theother side of the aforementioned cylindrical body fitted in the valvebore so as to support the above-mentioned rod body, and a push rodslidably fitted via a compression spring in an axial bore drilled in theaforementioned axial rod so as to bias the above-mentioned axial rodtowards the head portion of the poppet.

According to a ninth aspect of the present invention, there is provideda poppet valve device as described above in connection to the eighthaspect, which comprises a pressure chamber formed between theabove-mentioned push rod and the above-mentioned cylindrical body so asto push the aforementioned push rod towards the other side of theabove-mentioned cylindrical body against the compression spring, andexternal pressure feed means communicated with the above-mentionedpressure chamber via communication holes formed respectively in theabove-described cylindrical body and the above-described rod.

According to a tenth aspect of the present invention, there is provideda poppet valve device as described above in connection to the eighthaspect, which comprises a pressure chamber formed between theabove-mentioned push rod and the above-mentioned cylindrical body so asto push the aforementioned push rod towards the above-mentionedcylindrical body against the compression spring, and a passageway forcommunicating the above-mentioned pressure chamber via communicationholes formed respectively in the aforementioned cylindrical body and theaforementioned axial rod to the port formed in the above-described firstpoppet valve so as to communicate with the above-described pilot valve.

The above-mentioned and other objects, aspects and advantages of thepresent invention will become apparent for those skilled in the art fromthe following description and explanation with reference to theaccompanying drawings which disclose preferred embodiments conformableto a principle of the present invention as practical examples.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 through 4 are schematic cross section views of an essentialpart, illustrating first to fourth preferred embodiments of the presentinvention;

FIG. 5 is a schematic cross-section view of an essential part,illustrating a fifth preferred embodiment of the present invention; and

FIGS. 6 and 7 are cross-section views of different first poppet valveswhich are available in the fifth preferred embodiment illustrated inFIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, a number of preferred embodiments of the presentinvention will be explained with reference to the accompanying drawings.

As shown in FIG. 1, a first poppet valve A, a second poppet valve B anda pilot valve C are provided, and provision is made such that the firstpoppet valve A and the second poppet valve B are sequentially operatedto switch by operating the pilot valve C to operate.

The above-mentioned first and second poppet valves A and B arerespectively adapted to communicate or intercept a hydraulic actuatorsuch as, for example, a raising pressure chamber 1a in a boom cylinder 1of a power shovel with or from a tank 2, and the raising pressurechamber 1a and a lowering pressure chamber 1b of the boom cylinder 1 areadapted to be controllably fed with delivery pressurized oil of a pump 3via an operation valve 4.

The above-mentioned first poppet valve A is constructed in the followingmanner.

That is, in a valve bore 21 of a valve main body 20 are respectivelyformed a first port 22 communicating with the raising pressure chamber1a of the boom cylinder 1, a second port 23 communicating with the pilotvalve C and a third port 24 communicating with the tank 2, also in theabove-mentioned valve bore 21 is fitted and inserted a cylindrical body29, in the aforementioned cylindrical body 29 are formed an inlet port30 opening at the first port 22 and an outlet port 31 opening at thethird port 24, also in the cylindrical body 29 is slidably fitted andinserted a poppet 32 for communicating or intercepting its input port 30with or from its outlet port 31, in the above-mentioned poppet 32 isformed an axial bore 33 having a stepped configuration consisting of asmaller diameter bore 33a and a larger diameter bore 33b, and in theabove-described axial bore 33 is fitted and inserted a spool 34including a first land portion 34a having a smaller diameter and asecond land portion 34b having a larger diameter, so that between thespool 34 and the smaller diameter bore 33a is formed an annular chamber35, and between the larger diameter bore 33b and the second land portion34b is formed a first back pressure chamber 38a.

The above-described spool 34 butts against a front surface 37a of anaxial body 37 fixedly fitted and inserted in the aforementionedcylindrical body 29 due to a spring 36, and a second back pressurechamber 38b is formed between the front surface 37a and the rear surface32b of the poppet 32, the above-mentioned annular chamber 35 iscontrollably opened to the above-described inlet port 30 through avariable choke 44 consisting of an inflow port 39 of slit groove shapeformed in the poppet 32 and the first land portion 34a of the spool 34,also it communicates with the above-mentioned second port 23 through anoil hole 40 formed in the poppet 32 and an oil hole 42 formed in thesmaller diameter portion 41 and the cylindrical body 29, and theabove-described second back pressure chamber 38b communicates with theaforementioned second port 23 via a choke 43.

It is to be noted that the second poppet valve B is also similarlyconstructed. The above-described pilot valve C is constructed in thefollowing manner. That is, in a valve bore 51 of a valve main body 50are formed a first port 52 and a second port 53, also in the valve-bore51 is fitted and inserted a cylindrical body 54, in this cylindricalbody 54 is fitted and inserted a spool valve 37 for communicating orintercepting an inlet port 55 with or from an outlet port 56, the spoolvalve 57 is held at an intercepting position by a spring 58 and it isadapted to be moved to a communicating position by means of a solenoid59, the first port 52 communicates with the second ports 23 of theaforementioned first and second poppet valves A and B, the second port53 communicates with the tank 2, so that depending upon an amount of acurrent fed to the solenoid 59, an aperture area between the inlet port55 and the outlet port 56 is increase or decreased to controllablyincrease or decrease a flow rate of the flow from the inlet port 52 tothe tank 2 and thereby the pressure on the side of the inlet port 52 canbe regulated. In other words, a variable choke portion which iscontrolled depending upon an amount of a current fed to the solenoid 59,is provided.

Because of the above-described construction, pressurized oil in theraising chamber 1a in the boom cylinder 1 flows sequentially through thefirst port 22, the inlet port 30, the variable choke 44, the annularchamber 35, the oil hole 40, the smaller diameter portion 41 and the oilhole 42 to the second port 23 and flows out to the tank 2 through theinlet port 55 and the outlet port 56 of the pilot valve C, when acurrent is fed to the solenoid 59 of the pilot valve C and the inletport 55 and the outlet port 56 communicate with each other, hence apressure difference is produced between the front and the rear of thevariable choke 44, an inlet side pressure P₁ thereof acts upon ashoulder portion 32a of the poppet 32, and an outlet ride pressure P₀acts upon the second back pressure chamber 38b through the first backpressure chamber 38a and the choke 43.

Here, since the above-mentioned pressure difference is determineddepending upon the flow rate of the flow through the variable choke 44,and also the flow rate is determined by the aperture areas of the inletport 55 and the outlet port 56 of the pilot valve C, the above-describedpressure difference is determined by the aperture areas of the inletport 55 and the outlet port 56, that is, by the amount of the currentfed to the solenoid 59.

On the other hand, since the poppet 32 is subjected to a pushing forceF₁ directed to the right as viewed in this figure due to an inlet sidepressure P acting upon a shoulder portion 32a and a pushing force F₂directed to the left as viewed in this figure due to an outlet sidepressure P₀ within the first back pressure chamber 38a and the secondback pressure chamber 38b, as a result of the difference between apressure receiving area of the shoulder portion 32a and a pressurereceiving area of the first and second back pressure chambers 38a and38b as well as the aforementioned pressure difference, the poppet 32 ismoved rightwards, hence the seat surface 32b and the valve seat 30a areseparated from each other, and pressurized oil flows from the inlet port30 to the outlet port 31.

At this time, since the aperture area of the inlet port 30 and theoutlet port 31, that is, the flow rate to the tank 2 is proportional tothe above-mentioned pressure difference, the flow rate to the tank 2 iscontrolled by the amount of current feed to the solenoid 59, so that thedevice has a flow rate control function.

It is to be noted that under the condition shown in FIG. 1, the inletport 55 and the outlet port 56 of the pilot valve C are intercepted fromeach other and the above-described pressure difference is not produced,so that the poppet 32 is pushed to the left by a resilient force, andthe seat surface 32b is held in press contact with the valve seat 30a tointercept the inlet port 30 and the outlet port 31 from each other.

In the above explanation, a pressure balance condition of the poppet 32in the poppet valve is as follows: ##EQU1## where d₁ represents adiameter of the outlet port 31, d₂ represents a diameter of a spoolsmaller land portion 34a, and d₃ represents a diameter of a spool largerland portion 34b.

From the above-mentioned reasons, if the area ratio proportions whichdetermine the pressure balance of the first and second poppet valves Aand B are made to differ as follows, provision can be made such thatafter the first poppet valve A has been operated to switch, the secondpoppet valve B may be operated to switch: ##EQU2##

For instance, when d_(3A) =d_(3B) and d_(1A) =d_(1B) are fulfilled, itis only necessary to fulfil the relation of d_(2A) >d_(1B).

In other words, the area difference between the first back pressurechamber 38a and the second back pressure chamber 38b of the first poppetvalve A is made larger than that of the second poppet valve B so thatwhen the amount of current feed to the solenoid 59 is small, hence theflow rate is small and the pressure different between the front and therear of the variable choke 44 is small, the poppet 32 of the firstpoppet valve A may move to the right but the poppet 32 of the secondpoppet valve B may not move to the right, but when the amount of currentfeed to the solenoid 59 is further increased to make the flow rate largeand the pressure difference has become large, the poppet 32 of thesecond poppet valve B moves to the right.

As a result of such arrangement, the first and second poppet valves Aand B can be sequentially operated to switch by operating the singlepilot valve C to switch.

FIG. 2 shows a second preferred embodiment, in which a poppet 32 o afirst poppet valve A is made freely slidable along a smaller diametercylindrical portion 37b of an axial body 37, also provision is made suchthat a seat surface 32b is made to butt against a valve seat 30a bymeans of a spring 36 to intercept an inlet port 30 and an outlet port 32from each other, a diameter d_(1A) of the outlet port 31 and may bebalanced according to the following equation: ##EQU3##

As a result of such arrangement, if the pressure difference between thefront and the rear of the variable check 44 becomes larger than ΔP, thepoppet 32 of the first poppet valve A moves to the right, subsequently aspool 57 of a pilot valve C further moves to the right, hence a flowrate to the tank 2 is increased, a pressure P₀ within the back pressurechamber 38 is further lowered, and if it becomes lower than P₀ in theequation of balance for the second poppet valve B, then the poppet 32 ofthe second poppet valve B moves to the right.

FIG. 3 shows a third preferrred embodiment, wherein in a first poppetvalve A, a poppet 32 is fitted and inserted in a valve bore 21 of avalve body 20, this poppet 32 is biased by means of a spring 36 so thata seat surface 32b may butt against a valve seat 30a, thereby an inletport 30 and an outlet port 31 are intercepted from each other, a backpressure chamber 38 is communicated with a first port 52 of a pilotvalve C, and a pressure in the back pressure chamber 38 when the poppet32 of the above-mentioned first poppet valve A moves to the right, thatis, a valve-opening pressure P_(0A) is set lower than a valve-openingpressure P_(0B) of a second poppet valve B.

If such arrangement is made, when pressurized oil flows out from anoutlet port 56 of the pilot valve C to a tank 2, the pressure in thefirst port 52 is lowered, and the pressure in the back pressure chamber38 of the first poppet valve A is lowered.

And, if the pressure in the back pressure chamber 38 becomes lower thanthe valve-opening pressure P_(0A), the poppet 32 moves to the rightagainst the spring 36, and the first poppet valve A is operated toswitch.

If the pressure in the first port 52 is further lowered and becomeslower than the valve-opening pressure P_(0B) of the second poppet valveB, then a poppet 32 of the second poppet valve B is operated to switch.

It is to be noted that in FIG. 3, the outlet port 31 of the first poppetvalve A is connected to a lowering pressure chamber 1b of a boomcylinder 1 so that pressurized oil in a raising pressure chamber 1a maybe fed to the lowering pressure chamber 1b and the lowering pressurechamber 1b may not become negative pressure. In this connection, apressurized oil feed circuit for the boom cylinder 1 in the thirdpreferred embodiment illustrated in FIG. 3 is omitted.

FIG. 4 shows a fourth preferred embodiment, wherein in a head portion ofa poppet 32 of a first poppet valve A is formed a back pressure chamber61 to which pressure in an outlet port 31 is introduced through a narrowhole 60, and thereby the valve A is constructed in such manner that thepoppet 32 may be moved in the direction for intercepting an inlet port30 and the outlet port 31 from each other in response to the pressure inthe outlet port 31.

Furthermore, at a tip end portion of the poppet 32 is integrally formeda larger diameter portion 62 so that a force pushing the poppet valve 32to the right caused by the pressure at the outlet port acting upon aseat surface 32b of the poppet 32 may be offset.

If such arrangement is made, when a current has been fed to the solenoid59 of the pilot valve C, just as the above-described third preferredembodiment, the poppet 32 of the first poppet valve A moves to the rightand communicates the inlet port 30 with the outlet port 31, and furtherwhen the amount of current feed to the solenoid 59 has been increased,the poppet 32 of the second poppet valve B moves to the right andcommunicates the inlet port 30 with the outlet port 31, and so, thefirst poppet valve A and the second poppet valve B can be sequentiallyoperated to switch.

At the same time, the pressure at the outlet port 31 of the first poppetvalve A is introduced to the back pressure chamber 61 to move the poppet32 to the left and intercept the inlet port 30 from the outlet port 31,and so, the pressure at the outlet port 31 can be made to have apredetermined valve.

More particularly, the poppet 32 is subjected to a rightward force dueto the pressure acted upon the shoulder portion 32a, and a pressurereceiving area of the shoulder portion 32a is equal to ##EQU4##

Also, it is subjected to a leftward force due to the pressure acted uponthe back pressure chamber 38 and the back pressure chamber 61, and theirpressure receiving areas are equal to ##EQU5## and d_(2A) ² π,respectively.

And upon the shoulder portion 32a acts the pressure P₁ at the inlet port30, upon the back pressure chamber 38 acts the pressure P_(0B) reducedby a variable choke 44 of the second poppet valve B, and upon the backpressure chamber 38 acts the pressure P₀ at the outlet port 31.

Accordingly, the poppet 32 is balanced under the condition of: ##EQU6##and therefore, from the preceding equation, the following relation isderived: ##EQU7##

Here, since P_(0B) takes a value proportional to ##EQU8## which dependsupon the diameters of the respective portions of the second poppet valveB, it is determined by the second poppet valve.

Accordingly, the pressure P₀ at the outlet port 31 of the first poppetvalve A can be arbitrarily selected by determining the diameters of therespective portions.

It is to be noted that in the fourth preferred embodiment illustrated inFIG. 4 also, just like the third preferred embodiment illustrated inFIG. 3 a pressurized oil feed circuit for a boom cylinder 1 is omitted.

Next, a fifth preferred embodiment will be explained with reference toFIG. 5.

As shown in FIG. 5, a first poppet valve A, a second poppet valve 2 anda pilot valve C are provided, and the arrangement is such that byoperating the pilot valve C to switch, the first poppet valve A and thesecond poppet valve B can be sequentially operated to switch.

The above-mentioned first poppet valve A communicates or intercepts ahydraulic actuator, for instance, a raising pressure chamber 1a of aboom cylinder 1 with or from another hydraulic actuator, for instance, araising pressure chamber 10a of an arm cylinder 10, the above-mentionedsecond poppet valve B communicates or intercepts the raising pressurechamber 1a of the aforementioned boom cylinder 1 with or from a tank 2,and delivery pressurized oil of a pump 3 is adapted to be controllablyfed to the raising pressure chambers, 1a and 10a and the loweringpressure chambers 1b and 10b of the boom and arm cylinders 1 and 10,respectively, via operation valves 4 and 4'.

The aforementioned first poppet valve A is constructed in the followingmanner.

That is, in a valve bore 210 of a valve main body 200 are respectivelyformed a first port 220 communicating with the raising pressure chamber1a of the boom cylinder 1, a second port 230 communicating with thepilot valve C, and a third port 240 communicating with the raisingpressure chamber 10 of the arm cylinder 10, also in the above-mentionedvalve bore 210 is fitted and inserted a cylindrical body 290, in theaforementioned cylindrical body 290 are formed an inlet port 300 openingat the first port 220, an outlet port 310 opening at the third port 240,and a port 280 opening at the second port 230, also a poppet 320 forcommunicating or intercepting the inlet port 300 with or from the outletport 310 is slidably fitted and inserted in the cylindrical body 290,further an axial rod 330 is fixedly inserted therein, and a rod body 360is fitted and inserted over a blind bore 340 of the poppet 320 and ablind bore 350 of the axial rod to form a back pressure chamber 370 ofthe poppet 320, a middle portion in the axial direction of theabove-mentioned rod body 360 has a reduced diameter and forms an oilpassageway 380 jointly with the above-mentioned blind bores 340 and 350,a slit groove 390 formed in the poppet 320 and the above-mentioned backpressure chamber 370 are communicated with each other through this oilpassageway 380, also the slit groove 390 and a port 400 formed in theaxial rod 330 are communicated with or intercepted from each otherthrough the oil passageway 380, the port 400 communicates with theabove-mentioned port 280, a push rod 410 fitted and inserted in theabove-described axial rod 330 butts against an end surface of the rodbody 360 and also is pushed to the right as viewed in the figure by aspring 420, a pressure receiving chamber 430 pushing the push rod 410 tothe left communicates with the above-mentioned outlet port 310 through ahole 440 formed in the axial rod 330, a narrow hole 450 in the rod body,a blind bore 460 and a hole 470 in the poppet 320, the above-mentionedpoppet 320 is pushed to the left by a spring 480, hence a seat surface320a butts against a seat 290a, and thereby the inlet port 300 and theoutlet port 310 are intercepted from each other.

Since the first poppet valve A is constructed in the above-describedmanner, when the second port 230 is intercepted and pressurized oil inthe second port 230 does not flow, the pressures in the inlet port 300and in the back pressure chamber 370 become equal to each other, hencethe poppet 320 is pushed to the left by the spring 480 and interceptsthe inlet port 300 from the outlet port 310, resulting in the stateshown in FIG. 5.

Under this condition if the pressurized oil in the second port 230 flowsout to the tank 2, then the pressurized oil in the inlet port 300 flowsthrough the second port 230 to the tank 2, and at this time sincepressure drop occurs as choked at the communicating portion between theslit groove 390 and oil passageway 380, the pressure in the backpressure chamber 370 becomes lower than the pressure on the side of theinlet port 300. In other words, the communicating portion between theslit groove 390 and the oil passageway 380 forms a variable choke 490.

Thereby the poppet 320 is pushed to the right, hence the inlet port 300and the outlet port 310 communicates with each other and the pressurizedoil in the inlet port 300 flows out to the outlet port 310, but as thecommunication cross-section area is very small and the flow is chokedthere, the pressure on the side of the outlet port 310 becomes lowerthan the pressure on the side of the inlet port 300.

If the pressure on the side of the outlet port 310 becomes a presetpressure, the push rod 410 is pushed to the left against the spring 420by the pressure within the pressure receiving chamber 430, the rod body360 is pushed to the left against the spring 480 and intercepts the port400 from the oil passageway 380, so that the flow of pressurized oilfrom the inlet port 300 to the second port 230 disappears, the pressurein the back pressure chamber 280 rises and the poppet 320 is pushed tothe left to intercept the inlet port 300 from the outlet port 310.

The above-mentioned second port B is constructed in the followingmanner.

That is, in a valve bore 610 of a valve body 600 are respectively formeda first port 620 communicated with the raising pressure chamber 1a ofthe boom cylinder 1, a second port 630 communicated with the pilot valveC, a third port 640 communicated with a tank 2, in the above-describedvalve bore 610 is fitted and inserted a cylindrical body 690, in theaforementioned cylindrical body 690 are formed an inlet port 700 openingat the first port 630 and an outlet port 710 opening at the third port640, also a poppet 720 for communicating or intercepting the inlet port700 with or from the outlet port 710 is slidably fitted and insertedtherein, in the aforementioned poppet 720 is formed an axial bore 730having a stepped configuration consisting of a smaller diameter bore720a and a larger diameter bore 720b, in the above-mentioned axial bore730 is fitted and inserted a spool 740 having a first land portion 740awith a smaller diameter and a second land portion 740b with a largerdiameter, and an annular chamber 75 is formed between the spool 740 andthe smaller diameter bore 730b, while a first back pressure chamber 780ais formed between the larger diameter bore 730b and the second landportion 740b.

The above-mentioned spool 740 is made to butt against a front surface770a of an axial body 770 fixedly fitted and inserted in theabove-mentioned cylindrical body 690 by a spring 760 to form a secondback pressure chamber 780b between the rear surface 720a of the poppet720 and the spool 740, the above-mentioned annular chamber 750 iscontrollably opened at the aforementioned inlet port 700 through avariable choke 800 consisting of a slit-groove-shaped inflow port 790formed in the poppet 720 and the first land portion 740a of the spool740, also it communicates with the aforementioned second port 630through an oil hole 810 formed in the poppet 720 and an oil hole 830formed in the smaller diameter portion 820 and the cylindrical body 690,and also the aforementioned second back pressure chamber 380bcommunicates with the above-mentioned second port 630 via a choke 840.

Since the second poppet valve B is constructed in the above-describedmanner, like the above-described first poppet valve A, a pressuredifference is produced between the front and the rear of the variablechoke 800 by communicating the pressurized oil in the second port 630 tothe tank 2, the poppet 720 moves to the right, resulting incommunication of the inlet port 700 with the outlet port 710, andmoreover arrangement is made such that the pressure difference betweenthe front and the rear of the variable choke 800 when the poppet 720moves to the right may arise after the push rod 410 of theabove-mentioned first poppet valve A has been pushed to the left.

In other words, the poppet 320 of the first poppet valve A and thepoppet 720 of the second poppet valve B are pushed to the left by thepressures in the back pressure chamber 370 and in the first and secondback pressure chambers 780a and 780b, and pushed to the right by thepressures in the pressure receiving portions a and b, and since thesepressures are identical, by making area ratios of them different fromeach other, the poppet 720 of the second poppet valve B can be operatedin the above-described manner.

The above-mentioned pilot valve C is constructed in the followingmanner.

That is, the construction is such that a first port 520 and a secondport 530 are formed in a valve bore 510 of a valve main body 500, acylindrical body 540 is fitted and inserted in the valve bore 510, aspool valve 570 for communicating or intercepting an inlet port 550 withor from an outlet port 560 is fitted and inserted in this cylindricalbody 540, the spool valve 570 is held at an intercepting position bymeans of a spring 580, and it can be moved to a communicating positionby means of a solenoid 590, the first port 520 communicates with thesecond ports 230 and 630 of the above-described first and second poppetvalves A and B, the second port 530 communicates with the tank 2, alsodepending upon an amount of current feed to the solenoid 590 theaperture areas of the inlet port 550 and the outlet port 560 areincreased or decreased, and thereby a flow rate of the flow from theinlet port 520 to the tank 2 is controllably increased or decreased sothat the pressure on the side of the inlet port 520 can be regulated. Inother words, the pilot valve C includes a variable choke portion whichis controlled by the amount of current feed to the solenoid 590.

Since the above-described arrangement is made, if the flow rates of theflows flowing from the second ports 230 and 630 of the first and secondpoppet valves A and B to the tank 2 is increased by increasing thecommunication areas of the inlet port 550 and the outlet port 560according to the amount of current feed to the solenoid 590 of the pilotvalve C, then pressure differences are produced between the front andthe rear of the variable chokes 490 and 800, hence the poppet 320 of thefirst poppet valve A operates in the above-described manner, andthereafter the poppet 720 of the second poppet valve B operates in theabove-described manner.

Alternatively, the device could be constructed in such manner that asshown in FIG. 6 a pressure chamber 900 for pushing a push rod 410 to theright is formed, this pressure chamber 900 is communicated with externalpressure feed means 930 through a communication hole 910 formed in aaxial rod 330 and a communication hole 920 formed in a cylindrical body290, and pressurized oil may be fed into the pressure chamber 900 by theexternal pressure feed means.

If the device is constructed in such manner, the pressure at the outletport 310 when the push rod 410 moves to the right can be arbitrarilycontrolled.

Also, the device could be constructed in such manner that as shown inFIG. 7, the above-mentioned pressure chamber 900 is communicated with anoil passageway 280 through a communication path 940, and the pressure inthe back pressure chamber 370 is led to the chamber 900 to push the pushrod 410 to the right.

If such arrangement is made, the pressure at the outlet port 710 whenthe push rod 410 moves to the left can be made higher than that in thecase of FIG. 5.

We claim:
 1. A poppet valve device comprising: at least two, first andsecond poppet valves, each of which is constructed in such manner that apoppet for communicating or intercepting an inlet port and an outletport formed on one side of a cylindrical body fitted within a valve bodymay be moved towards a communicating position by a pressure on the inletport side acting upon a pressure receiving portion, while it may bemoved towards an intercepting position by a pressure acting upon a backpressure chamber; and a pilot valve which connects the back pressurechambers of the respective ones of said plurality of poppet valves to atank, and which includes a variable choke portion controlled by anexternal input signal so that the pressures in the respective backpressure chambers when the respective poppets in said respective poppetvalves are moved to the positions for communicating the respective inletports with the respective outlet ports are individually regulated.
 2. Apoppet valve device as claimed in claim 1, wherein the poppet of saidfirst poppet valve is mounted so as to be freely slidable along asmaller diameter cylindrical body of an axial body fitted within saidcylindrical body from the other side of said cylindrical body, and isbiased towards said intercepting position by a resilient force of acompression spring interposed between said axial body and said poppet,and the inner diameters of the respective ones of said outlet port andsaid poppet are made identical.
 3. A poppet valve device as claimed inclaim 1, wherein a valve-opening pressure in the back pressure chamberwhen the poppet in said first poppet valve is moved towards saidcommunicating position, is set lower than a valve-opening pressure ofsaid second poppet valve.
 4. A poppet valve device as claimed in claim3, wherein the inlet port of said first poppet valve communicates with aboom raising pressure chamber in a boom cylinder of a constructionmachine such as a power shovel, and the outlet port communicates with aboom lowering pressure chamber in said boom cylinder.
 5. A poppet valvedevice as claimed in claim 1, wherein the poppet in said first poppetvalve includes a back pressure chamber to which the pressure at itsoutlet port is introduced via a narrow hole drilled at the head portionof the poppet so that said poppet may be biased towards the interceptingposition by the pressure at the outlet port, and a larger diameterportion formed integrally at the tip end portion of said poppet valve soas to offset a pressing force in the direction directed to thecommunicating position of said poppet caused by the pressure at theoutlet port acting upon a seat surface of the poppet in said firstpoppet valve.
 6. A poppet valve device as claimed in claim 5, whereinthe inlet port of said first poppet valve communicates with a boomraising pressure chamber in a boom cylinder of a construction machinesuch as a power shovel, and the outlet port communicates with a boomlowering pressure chamber in said boom cylinder.
 7. A poppet valvedevice as claimed in claim 1, which comprises two, first and secondpoppet valves whose back pressure chambers are communicated with theirtank sides so that the pressure acting upon the respective back pressurechambers may serve as a tank side pressure and also communicated withthe inlet port sides via chokes, and a pilot valve including variablechoke portions provided between said first and second poppet valves anda tank and controlled by an external input signal, wherein theconstruction is such that if the outlet side pressure of said firstpoppet valve becomes a preset pressure or higher, the inlet port and theoutlet port of said first poppet valve are intercepted from each other,whereas when the pressure in the back pressure chamber in said secondpoppet valve causes the poppet in said first poppet valve to come at thecommunicating position, if it becomes a lower pressure than the pressurein the back pressure chamber in the first poppet valve, the inlet portand the outlet port of said second poppet valve may be communicated witheach other.
 8. A poppet valve device as claimed in claim 1, wherein saidfirst poppet valve includes a rod body fitted in an inner bore of thepoppet from the base end side of said cylindrical body fitted in aninner bore of said poppet from the base end side of the same poppet viaa compression spring, an axial rod inserted from the other side of saidcylindrical body fitted in the valve bore so as to support said rodbody, and a push rod slidably fitted via a compression spring in anaxial bore drilled in said axial rod so as to bias said axial rodtowards the head portion of the poppet.
 9. A poppet valve device asclaimed in claim 8, which comprises a pressure chamber formed betweensaid push rod and said cylindrical body so as to push said push rodtowards the other side of said cylindrical body against the compressionspring, and external pressure feed means communicated with said pressurechamber via communication holes formed respectively in said cylindricalbody and said axial rod.
 10. A poppet valve device as claimed in claim8, which comprises a pressure chamber formed between said push rod andsaid cylindrical body so as to push said push rod towards the other sideof said cylindrical body against the compression spring, and apassageway for communicating said pressure chamber via communicationholes formed respectively in said cylindrical body and said axial rod tothe port formed in said first poppet valve so as to communicate withsaid pilot valve.